1. Technical Field
The present invention relates to a power generation method using molten carbonate fuel cells which directly convert chemical energy of fuel into electric energy.
2. Background Art
A conventional fuel cell system is generally comprised of a stack of fuel cell elements and separators interposed between two adjacent fuel cell elements. Each fuel cell generally includes an electrolyte plate (tile), a cathode (oxygen electrode) and an anode (fuel electrode). In case of molten carbonate fuel cell, the electrolyte plate includes a porous substance soaked with molten carbonate, and the cathode and the anode sandwich the electrolyte plate. Oxidizing gas is fed to the cathode and fuel gas is fed to the anode in order to cause power generation.
The fuel gas used for the fuel cell is generally reformed by a reformer. FIG. 2 of the accompanying drawings shows a power generation system using a molten carbonate fuel cell in which natural gas is used as the fuel to be reformed (referred to as "raw material gas"). Before feeding oxidizing gas to a cathode 2 of a fuel cell 1, air A delivered by blower 4 is preheated by an air preheater 5 in an air feed line 6. Part of the air A is introduced to a reformer 8 by a branch line 7. Gases discharged from the cathode 2 are introduced to a turbine 10 by a line 9 and then expelled via the air preheater 5. On the other hand, natural gas NG (for example, methane) which is fed to the anode 3 and reformed therein is pressurized by a blower 18 and forced to flow through a natural gas preheater 11 and a desulfurizer 23 before reaching the reformer 8. The natural gas NG (raw material gas) is reformed in the reformer 8 and fed to the anode 3 from a fuel gas line 19. Gases AG discharged from the anode 3 (called "anode exhaust gas") contain moisture that has to be removed. The moisture (steam) separated from the anode exhaust gas is mixed with the natural gas NG before an entrance of the reformer 8. To this end, the anode exhaust gas AG is led to the natural gas preheater 11 from an anode exit gas line 20, and cooled and condensed by a condenser 12 and the gas component of the anode exhaust gas is separated from the moisture component by a gas-liquid separator 14 so as to separate it into gas G and water. The gas G is introduced to the reformer 8 by a blower 13 and used for combustion. The water (H.sub.2 O) is pressurized by a pump 15 and transferred to a vaporizer 16. The water becomes steam in the vaporizer 16 and flows in a steam line 17 to merge with the natural gas NG of the natural gas introduction line 22 on the reformer entrance side. Gases discharged from the reformer 8 which contain CO.sub.2 flow through an exhaust gas line 21 and enter the cathode 2 with the air of the air feed line 6.
However, this type of power generation system has drawbacks; the steam required for the reforming reaction is made from water. Thus, the vaporizer 16 is a requisite. Further, the water to be introduced to the vaporizer 16 should be high-purity water so that a water treatment equipment (generally a water treatment equipment adapted to prepare boiler-water, i.e., a gas-liquid separator) is necessary.